Cathode ray tube, getter, and method of gettering



Feb. 11, 1964 w. L. c. HUI ETAL 3,121,182

CATHODE RAY TUBE, GETTER, AND METHOD OF GETTERING Filed Nov. 21, 1961 I s 9 J. I

\ I 1 INVENTORS F M104 1. C. 190/ gi 82 Y JOHN/4. 51 55 147' TOfA/E) United States Patent 3,121,182 (IATHODE RAY TUBE, GETI'ER, AND METHOD 0F GETI'ERING William L. C. Hui, Princeton, NJL, and John A. Files,

Arnhoy, Ind, assignors to Radio (Iorporation of America, a corporation of Delaware Filed Nov. 21, 1961, Ser. No. 153,324 13 Claims. (Cl. 313178) This invention relates to cathode ray tubes and to a getter and method of gettering cathode ray tubes.

Among the objects of this invention are: the provision of an improved cathode ray tube of reduced length for Wide angle deflection operation, the provision of a new and improved getter for such a tube, and the provision of a new and improved method of activating a getter in a cathode ray tube.

Some cathode ray tubes, such as television picture tubes, include an envelope having a neck section in which an electron gun is disposed. In order to obtain a large area gettering surface, a getter structure is usually mounted on the end of the electron gun nearest the phosphor screen and the getter vapors directed out of the envelope neck and onto the other walls of the tube. Getters for such tubes usually comprise a quantity of vaporizable gettering material contained in a channel-like support member. The channel support remains in place after the getter is vaporized.

In order to make the cathode ray' tube as short as possible, it is desired to begin deflection of the electron beam as soon as possible along its axial path. However, the presence of the channel-like support member precludes excessive deflection in the vicinity of the getter, lest the beam be obstructed by the support.

One form of getter particularly troublesome in this respect is that which is widely used by the industry because of its good gettering capabilities. Its channel support comprises a ring which is mounted coaxially with the electron gun. In operation of the tube, the electron beam is projected through the central opening of the ring. In order to permit RF heating of the getter to vaporize it, the ring is mounted in axially spaced relationship from the end of the gun by a support bracket. Such axial spacing further adds to the necessary length of the tube.

According to one feature of this invention, the difiiculty of beam obstruction by the getter support is obviated and shorter tube lengths permitted by use of a removable getter. The novel getter is mounted in a cathode ray tube in a location to which the electron beam of the tube can be directed. For example, this may be directly in the beam path across the aperture of one of the electrodes of the electron gun. It comprises a sheet of thin vaporizable metal foil into which a cuplike depression has been formed. A suitable gettering material, e.g., barium metal, is disposed in the cup and a protective coating such as a thin film of evaporated aluminum is provided over the exposed surface of the gettering material.

In accordance with another feature of this invention, the novel getter of the invention is at least partially vaporized by a heating thereof by' bombarding it with an electron beam generated by the gun on which the getter is mounted. A given intensity of beam current is used to heat the get-tering material to a temperature sufiicient to vaporize it and cause it to deposit on internal surfaces of the tube. The beam current intensity is then increased to burn away, or vaporize (remove), the sheet metal cup member which serves as the support container for the gettering material.

Although this invention is particularly useful in wide angle deflection tubes, it is not limited to use in such tubes.

In the drawings:

FIG. 1 illustrates a cathode ray tube in partial section with parts broken away and embodying my invention;

FIGS. 2 and 3 are enlarged longitudinal section and end plan views, respectively, of a portion of the cathode ray tube of FIG. 1 showing the getter and the electrode on which it is mounted; and

FIGS. 4 and 5 are end plan views of modifications of the structure illustrated in FIG. 3.

In FIG. 1, an electron tube 10' includes a vacuumtight envelope 12 comprising a neck section 14-, a faceplate 16, and an interconnecting funnel section 18 (only the end portions of which are shown). An electron gun 20 in the neck 14 is adapted .to project an electron beam along a beam path onto a phosphor screen 22 .on the faceplate 16. The phosphor screen 22 may be of any suitable type, such as one comprising a layer of phosphor material on the faceplate 16 with a superimposed film of evaporated aluminum thereupon. A conductive coating 24 is provided on the internal surface of the funnel 18 and is connected to the phosphor screen 22 and to one of the electrodes of the electron gun 2% in a manner explained more fully hereinafter. A high voltage contact terminal, indicated schematically by the arrows 26, is provided for applying a suitable voltage to the coating 24 and to the electrode to which it is connected. The neck section 14 is closed at its free end with a stem and base structure 23, which includes a plurality of leadin conductors 30 for applying suitable voltages to the electrodes to the electron gun '20.

The electron gun 20' of the tube 10 comprises a plurality of coaxial, tubular, electrodes having aligned central openings therethrough including a control grid 32, a screen grid 34, a first anode 35, a focusing electrode 36, and a second anode 38. The first and second anodes 35 and 38 are electrically tied together internally of the tube 19 by a connector (not shown). The electordes 32, 34, 35, 36, and 38 are mounted in coaxial spaced relationship along a pair of insulator, e.g., glass, rods 40 by U-shaped mounting studs 41 which are fixed to the electrodes and embedded in the insulator rods. A tubular cathode 42 is mounted in a centrally apertured insulator disk 4 which is in turn fixed Within the tubular control grid 32. The cathode 42 is provided with a closed end 46 which is coated with an electron emissive material.

In the operation of the tube 10, electrons are emitted from the cathode 42 and converged to a first crossover in the vicinity of the central aperture 48 of the screen grid 34. This crossover is then imaged on the phosphor screen 22 by an electron lens formed by the electrodes 35, 36 and 38. The second anode 38 is provided with a radial flange 54, which extends outwardly to within a very short distance from the wall of the envelope neck 14. A plurality of spring snubbers 56 are fixed to the flange 54 and bear outwardly against the conductive coating 24, which extends slightly into the neck 14. The snubbers 56 serve both to provide an electrical connection to the first and second anodes 35 and 38, and to support one end of the electron gun 29 centrally within the neck 14. The other end of the electron gun 2G is supported (not shown) on some of the lead-in conductors 30.

A heat removable getter 60 is mounted on the flange 54 of the second anode 38 across the central tubular opening 61 thereof. FIGS. 2 and 3 illustrate in enlarged detail the electrode 38 and getter 60. The getter 60 comprises a sheet 62 of vaporizable conductive material such as a metallic ribbon. The conductive sheet 62 is formed with a cup-like depression 64 pressed therein which contains a charge, or quantity, of suitable gettering material 66. The gettering material 66 is preferabl'y of a type, such as metallic barium, which can be completely vaporized without leaving a residue of oxides or other ash. A protective film 68, such as an evaporated aluminum film, may be provided over the gettering material 66 to insure that the gettering material is maintained in a clean, chemically unreacted state until such time as it is incorporated in the cathode ray tube it) and deposit.

The getter 66' may be attached to the flange 54 in any suitable and convenient manner. An electrical contact should exist between the getter and the flange so that a suitable voltage can be applied to the getter during the vaporizing thereof, and so that the bombarding electrons collected by the getter can be conducted away. On the other hand, the less the thermal conductivity between the cup portion 64 of the getter land the supporting flange 54, the easier it is to heat the getter to vaporizing temperatures. A simple spot welding of the getter 69 to the flange 54 has been found to be suitable.

If desired, thermal conductivity can, for example, be reduced by reducing the physical contact between the getter and the flange 54 or by reducing the thickness or width of the support foil 62 at points between the supporting flange 54. FIG. 4 shows such a getter '70. The getter 70 comprises a sheet support member '72 formed with a cup 74 in the central portion therein and having narrow support legs (end portions) 76 which contact,

and are Welded to, the flange 5 4. The narrow legs 76' provide both low thermal conductivity from the cup to the ends of the legs and small area contact between the legs and the flange 54. Thermal conductivity is thus minimized from the cup 74 to the flange 54.

In the drawings generally, and FIG. 2 specifically, the relative thicknesses of the support ribbon 62, the gettering material 66, and the protective film 68 are not intended to be to scale. Some specific dimensions of these parts are hereinafter set forth in more detail. The support ribbon 62 should be of sufiicient thickness to adequately sup-port the gettering material 66 and to render it Weldable to the electrode 38, but yet thin enough to permit it to be vaporized by bombardment by an electron beam from the electron gun 2h. The protective film 68 need be only thick enough to protect the gettering material 66 from the atmosphere.

FIG. 5 illustrates a modification of the getter 6t} illustrated in FIGS. 2 and 3. In FIG. 4 a getter St! is illustrated which comprises a conductive support sheet 82 which completely closes the opening 61 of the electrode 38. The getter 88' of FIG. 4 is similar to the getter 60 of FIGS. 2. and 3 in that the conductive sheet is formed with a depresison 84 which contains a vaporizable getter material over which a protective film has been provided.

Since the support sheet 82 of the getter 80 completely covers the opening 61, the sheet 82 and electrode flange 54 effectively shield the electron gun from the portion of the tube 10 into which the getter vapors are directed Such shielding prevent-s vaporized getter material from being deposited on parts of the gun and thus giving rise to undesired stray emisson. The prevention of stray emission by a sheet of metal overlying the electron beam opening in an electrode in a cathode ray tube is described in copending application, Serial No. 76,287 of Robert E. Benway, filed December 16, 1960, and assigned to the assignee of this invention.

One example of the lgetter 60 as described above may be made as follows. Small pellets of metallic barium weighing 40 to 90 milligrams are first cut to size and stored under oil to maintain their metallic character. A Nichrome ribbon one-half mil in thickness and 150 mils in width is formed with a depression 64 of a size suitable to hold the desired barium pellet. The Nichrome ribbon 62 is then mounted between two electrodes in an evaculable chamber. A barium pellet is selected and washed in petroleum ether to remove the oil therefrom.

activated (vaporized) to provide the gettering.

i The pellet is then disposed in the cup-like depression 64 of the ribbon, the evacuable chamber closed, and evacuated to a pressure of approximately 5x10 mm. of mercury. A current is then passed through the ribbon to heat it and thereby melt the barium pellet so that it settles into the cup 64 and excludes any free space there from. A film of aluminum of, for ex ample, 2000' to 4000 Angstroms thick is then evaporated onto the top surface. of the melted barium 66 and onto at least a portion of the" Nichrome ribbon 62 to provide the protective film 68. In order to fabricate the getter by this method, the support sheet 62 should be of a suitable size and have suitable conductivity to permit its being electrically heated. The one-half mil thick, mil wide ribbon ofNichrome alloy has been found to be quite satisfactory in this respect. The fabrication procedure described in the preceding paragraph lends itself well to simultaneous fabrication of a number of getter units which are all mounted between the same two electrodes in the vacuum chamber. When the barium pellet is melted and settles into the cup-like depression 64, the Nichrome ribbon 62 is immediately cooled. This cooling prevents the melted barium of one getter from being further heated and subsequently vaporized before the barium pellet of another getter is adequately melted.

After the getter is fabricated and mounted into the cathode ray tube 10, the barium charge 66 of the getter 6b is vaporized with an electron beam generated by the gun 2t? to deposit a gettering film of barium onto the internal surface of the envelope 12. The electron beam is then increased in intensity to burn awvay or vaporize (and thus remove) the sheet support member 62 of the getter.

A getter 60 as specifically detailed above (comprising a support member 62 of one-half mil thick and 150 mils wide Nichrorne ribbon) mounted on the electron gun 24) can, for example, be activated and removed as follows. The electron gun 2.0 is energized with the cathode and control grid at zero volts, the screen grid at 360 volts, the first and second anodes at 18,000 volts, and the focus electrode adjusted at a point between zero and 400 volts to produce a small diameter beam of electrons at the getter 6! An operating voltage of about 6.3 volts is applied to the indirectly heated filament (not shown) of the cathode to heat the cathode to about 850 C. An electron beam of approximately 350 to 500- micro amperes is thus developed and impinges on the cup 64 of the getter 60. Volatilization of the barium charge 66 begins after about 30 seconds of electron bombardment and in about '60 seconds the barium has been completely vaporized and deposited on the wall of the envelope 12.

The tube 10 is then subjected to fan aging processing according to standard or known industry procedures to enhance maximum cathode emission capabilities. For example, the filament voltage is raised to about 13.5 volts and maintained there for about 1.5 minutes. This results in the cathode temperature being raised from about 850 C. to about 1200 C. During this high cathode temperature period, emission of from 15 to 20* milliamperes is established from the entire surface of the cathode coating and is collected by the other electrodes of the gun, all of which are electrically connected together either internally or externally of the tube.

ture of from 900 C. to 950 C. Operation at this tem perature is maintained for 27 to 30 minutes to complete the aging of the tube.

After the tube has been aged as described in the preceding paragraph, a standard filament voltage of 6.3 volts and electrode potentials Ias set forth above will produce an electron beam current of from 1000 to 1500 micro amperes. Such a current is thus generat d by the electron gun 20 and is deflected, such as by a conventional magnetic yoke, back and forth over the support member 62 to vaporize it and thus remove it from the path which the electron beam traverses during normal operation of The filament voltage is then adjusted to about 8.5 volts to produce a cathode temperathe tube 14 As a result only small remnants of the getter support member 62 are left attached to the flange 54, and these are out of the normal path of the electron beam.

During electron bombardment of the getter 60 to vaporize the barium charge 66, it is not necessary that the electron beam be deflected back and forth, or scanned, over the area of the getter. However, subsequently, when the getter support member 62 is heated and vaporized, it is advisable that the electron beam be then scanned over the surface of the member 62 so as to more completely vaporize all portions thereof and to avoid impingement of the electron beam at a fixed point on the luminescent screen of the tube for an extended period of time and thus possibly cause injury to the screen.

What is claimed is:

1. The method of gettering an electron tube having an electron gun, said method comprising mounting a charge of vaporizable gettering material in said electron tube and heating said material with a beam of electron from said electron gun to vaporize said material.

2. The method of gettering an electron tube having an electron gun, said method comprising the steps of mounting a getter including a charge of vaporizable gettering material in said electron tube, generating a beam of electrons with said gun, and directing said beam to bombard said getter with said beam to heat said getter and vaporize said gettering material therefrom and deposit it on surfaces within said tube.

3. The method of gettering a cathode ray tube having an electron gun including a plurality of electrodes having aligned central opening therein adapted to pass an electron beam generated by said gun, said method comprising the steps of mounting across the central opening of one of said electrodes a getter including a sheet metal support member having a cupped depression containing gettering material, generating a given intensity electron beam with said gun, directing said given intensity beam to bombard said getter and thereby vapor-ize said gettering material and deposit it on surfaces within said tube, and then increasing the intensity of said beam to provide a beam of higher intensity, and directing said higher intensity beam to bombard said getter support member to vaporize at least a portion thereof overlying the central opening of said one of said electrodes.

4. The method of gettering a cathode ray tube having an electron gun including a plurality of electrodes having aligned central openings therein adapted to pass an electron beam generated by said gun, said method comprising the steps of mounting across the central opening of one of said electrodes 21. getter including a sheet metal support member having a cupped depression containing gettering material, generating a given intensity electron beam with said gun, directing said given intensity beam to bombard said getter and thereby vaporize said gettering material and deposit it on surfaces within said tube, and then increasing the intensity of said beam to provide a beam of higher intensity, and directing said higher intensity beam to bombard said getter support member to vapor-ize at least a portion thereof overlying the central opening of said one of said electrodes, said higher intensity beam being scanned over said portion of said getter support member during the electron bombardment and vaporization thereof.

5. The method of gettering an electron tube having an electron gun adapted to project an electron beam along a path, said method comprising the steps or" fabricating a getter by mounting between two electrodes in an evacuable chamber a length of metallic ribbon formed with a cupped depression centrally thereof, depositing a quantity of a vaporizable gettering material within said cupped depression, closing said chamber, evacuating said chamber, passing an electric current through said ribbon to melt said gettering material and settle it into said depression, evaporating a film of protective material over the exposed surface of said gettering material to complete 6 the fabrication of said getter, removing said getter from said chamber, mounting said getter in said tube in said beam path, evacuating and sealing said tube, generating a beam of electrons with said gun, directing said beam along said path to bombard said getter with said beam to heat said getter and thereby vaporize said gettering material and deposit it on surfaces within said tube, thereafter increasing the intensity of said electron beam, and directing said increased intensity beam along said beam path upon the support member of said getter to vaporize and thereby remove at least a portion of said support member from said beam path.

6. A cathode ray tube comprising an evacuated envelope; an electron gun for projecting an electron beam along a path within said envelope; and remnants of a getter support attached to said gun, a part of said getter support having been vaporized to remove said part from said path and leave said remnants.

7. A cathode ray tube comprising an evacuated envelope, an electron gun within said envelope including a plurality of aligned electrodes which are adapted to project an electron beam and which have central openings therein through which said beam passes, and attached to one of said electrodes, the remnants only of a getter support comprising a metallic sheet adapted to support a charge of gettering material and be mounted on said one electrode across the opening therein.

8. A cathode ray tube comprising an evacuated en velope, an electron gun Within said envelope, said gun including a plurality of electrodes having aligned central openings therethrough through which an electron beam generated and projected by said gun passes, and getter comprising a ribbon of metal having a cupped depression formed therein and a charge of getter material in said cupped depression, said getter being mounted at the end portions of said ribbon on one of said electrodes and being disposed across the opening through said one electrode in the path of said beam, said end portions of said ribbon being narrow relative to the central cupped portion thereof whereby thermal conductivity from said getter to said one of said electrodes is minimized.

9. A cathode ray tube comprising a vacuum-tight envelope, an electron gun Within said envelope and including a plurality of electrodes having aligned openings therethrough through which an electron beam generated by said gun passes, and a getter comprising a sheet metal support member formed with a cupped depression therein and mounted on one of said electrodes across the opening therethrough, and a quantity of gettering material contained within said cupped depression.

10. An electron tube comprising a vacuum-tight envelope, an electron gun within said envelope adapted to develop and project an electron beam along a beam path, and a getter mounted on said gun in said beam path.

11. An electron tube comprising a vacuum-tight envelope, an electron gun within said envelope for projecting an electron beam along a beam path, and a getter mounted within said tube in said beam path, said getter comprising a support member and a quantity of gettering material supported by said support member, said gettering material being vaporizable by bombardment of said getter with a given intensity electron beam generated by said gun, said support member being vaporizable by bombardment thereof with a higher intensity electron beam from said gun, whereby said getter can be bombarded with an electron beam to first vaporize and redeposit said gettering material and then vaporize said support member to thereby remove said getter from said beam path.

12. A cathode ray tube comprising a vacuum-tight envelope, an electron gun for projecting an electron beam within said envelope and a getter mounted within said envelope in a location such that said beam can be directed to bombard said getter, said getter including a quantity of gettering material vaporizable by electron bombardment of said getter by said beam.

13. A cathode ray tube comprising a vacuum-tight envelope, an electron gun Within said envelope and including a plurality of electrodes having aligned openings therethrough through which an electron beam generated by said gun passes, and sheet metal mounted on one of said electrodes out of the path of the electron beam of References Cited in the file of this patent UNITED STATES PATENTS Szegho July 15, 1958 Sheldon May 12, 1959 

8. A CATHODE RAY TUBE COMPRISING AN EVACUATED ENVELOPE, AN ELECTRON GUN WITHIN SAID ENVELOPE, SAID GUN INCLUDING A PLURALITY OF ELECTRODES HAVING ALIGNED CENTRAL OPENING THERETHROUGH THROUGH WHICH AN ELECTRON BEAM GENERATED AND PROJECTED BY SAID GUN PASSES, AND GETTER COMPRISING A RIBBON OF METAL HAVING A CUPPED DEPRESSION FORMED THEREIN AND A CHARGE OF GETTER MATERIAL IN SAID CUPPED DEPRESSION, SAID GETTER BEING MOUNTED AT THE END PORTINS OF SAID RIBBON ON ONE OF SAID ELECTRODES AND BEING DISPOSED ACROSS THE OPENING THROUGH SAID ONE ELECTRODE IN THE PATH OF SAID BEAM, SAID END PORTIONS OF SAID RIBBON BEING NARROW RELATIVE TO THE CENTRAL CUPPED PORTION THEREOF WHEREBY THERMAL CONDUCTIBITY FROM SAID GETTER TO SAID ONE OF SAID ELECTRODES IS MINIMIZED. 